1. Field of the Invention
This invention is concerned with a tape cassette for metering the amount of typewriter correction tape that is fed from a correction tape cassette to a typewriter print point, and more particularly, with such a system in which the amount of typewriter correction tape that is fed to the print point is relatively constant regardless of the amount of tape on the take-up spool. The metering system also includes a correction tape feed mechanism that varies the amount of correction tape that is fed to the print point in accordance with the type of correction tape.
In a typical correction tape system for use in a typewriter, the correction tape extends from a supply spool to a position below the typewriter print point and then to a take-up spool. In a correction tape cassette system, such as the present invention, the supply spool, correction tape, and take-up spool are all housed in a cassette which is mounted on a cassette rocker. The cassette rocker is carried by and pivotable on a print wheel and ribbon carrier that is moveable along a line of type. When a character is to be deleted during an error correction step, the cassette rocker is pivoted upwardly to move the correction tape to the print point for the subsequent character deletion step.
Prior to use, a fresh, correction tape will be located almost entirely on the cassette supply spool (i.e. the diameter of the correction tape on the supply spool will be at its maximum), while the amount of correction tape on the take-up spool will be at its minimum. After each correcting operation, a drive means rotates the take-up spool to pull fresh correction tape from the supply spool and, in this manner, fresh tape is presented at the print point. As the correction tape is pulled from the supply spool, the amount (and diameter) of the correction tape on the supply spool is reduced, and the amount (and diameter) of the correction tape on the take-up spool is increased.
In order to reduce the amount of correction tape wastage, it is desirable to move only the required constant amount of correction tape to the typewriter print point. If, however, the take-up spool rotates the same amount each time a correction operation occurs, the amount of correction tape moved across the typewriter print point will not be constant, but will vary, because of the variations in the diameter of the correction tape on the take-up spool. For example, for the same amount of correction tape spool rotation, a smaller diameter of correction tape on the take-up spool will cause a lesser amount of correction tape to be fed to the typewriter print point than will a larger diameter of correction tape on the take-up spool. The present invention is concerned with a system for varying the amount of the take-up spool rotation in accordance with the diameter of correction tape on the take-up spool, so that the required constant amount of correction tape is moved across the typewriter print point regardless of the diameter of correction tape on the take-spool.
The present invention is also concerned with a system for metering the proper amount of correction tape that is fed to the print point in accordance with the type of the correction tape utilized in the cassette. There are, for example, in present usage, at least two types of typewriter correction tapes. One type is commonly referred to as "lift-off" tape. In operation, the lift-off tape is raised to the typewriter print point and the character on the type element which corresponds to the character to be deleted is positioned to strike the lift-off tape. Typewriter actuating means causes the type element to strike the lift-off tape against the unwanted character and, upon withdrawal of the lift-off tape from the paper, the tape lifts the unwanted character from the paper.
The other type of typewriter correction tape is commonly referred to as "cover-up" tape. In operation, the cover-up tape is raised to the typewriter print point and the character on the type element which corresponds to the character to be deleted is positioned to strike the cover-up tape. Typewriter actuating means causes the type element to strike the cover-up tape against the unwanted character and, upon the element striking the cover-up tape against the unwanted character, a powdery substance on the cover-up tape is transferred to and covers up the unwanted character.
Both the lift-off tape and cover-up tape may be housed within cassettes, and both may be used in the same typewriter, the choice of correction tapes being generally dependent upon the characteristics of the print ribbon being used for the printing operation. It is known that the amount of lift-off correction tape that must be fed to the print point to effectively lift off an unwanted character is less than the amount of cover-up correction tape that must be fed to the print point to effectively cover up an unwanted character. If, therefore, the typewriter correction feed mechanism always fed an amount of correction tape adequate for cover-up correction tape, it would feed an excessive and wasteful amount of lift-off tape when lift-off tape, and not cover-up correction tape, was present in the typewriter. On the other hand, if the typewriter correction feed mechanism always fed an amount of correction tape adequate for lift-off correction tape, it would feed an insufficient amount of cover-up tape when cover-up tape, and not lift-off tape, was present in the typewriter.
The present invention provides an improved correction tape metering system whereby the amount of tape that is fed is dependent on the diameter of correction tape on the take-up spool and is dependent upon the particular type of typewriter correction tape that is being utilized in the typewriter operation.
2. Prior Art
An example of a typewriter print ribbon metering device is disclosed in U.S. Pat. No. 4,302,118. Means are provided on the cassette for indicating whether the content of the cassette includes a carbon or cloth ribbon. Upon the cassette being inserted into the typewriter, the correct feed and ribbon lift mechanism is automatically selected to minimize ribbon wastage.
An example of a prior art correction tape feed mechanism is shown in U.S. Pat. No. 4,616,945 wherein oscillation of the correction tape cassette operates a cam follower operated pawl and ratchet for feeding the correction tape.
A prior art typewriter ribbon feed mechanism, which is designed to achieve a nearly constant speed, is disclosed in U.S. Pat. No. 3,677,486. The device includes a camming lug which detects the changing diameter of ribbon on the ratcheted ribbon spool, and reduces the angular distance that a reciprocating pawl engages the spool as the ribbon diameter increases.